1. Field of the Invention
The present application relates to compositions comprising a combination of a bifunctional alkylating agent and DNA repair inhibitors and use of the compositions in treating cancer, in particular drug resistant cancer.
2. Description of the Related Arts
DNA alkylating agents, commonly used as chemotherapeutic drugs for treatment of a variety of pediatric and adult cancers [1], exert their cytotoxic effects by directly interacting with DNA in a way that leads to DNA lesions. There are two types of DNA alkylating agents, monofunctional and bifunctional. Mechlorethamine, a bifunctional nitrogen mustard alkylating agent, was the first antitumor drug introduced into clinical practice more than 50 years ago [2]. Currently, a variety of bifunctional alkylating agents, such as the nitrogen mustards (e.g., melphalan [3]), nitrosoureas (e.g., carmustine [4]), alkyl sulfonates (e.g., busulfan [5]), aziridines (e.g., thiotepa [6]), platinum drugs (e.g., cisplatin [7]), and the natural product mitomycin C (MMC) [8], are still widely used for treatment of patients with malignant diseases. Although monofunctional alkylating agents mainly form genotoxic monoadducts to further induce mutagenic and carcinogenic DNA lesions, bifunctional alkylating agents form monoadducts, intrastrand crosslinks, and interstrand crosslinks (ICLs) on DNA, and also form DNA-protein crosslinks [9]. ICLs cause replisome dissociation and collapse, and subsequently induce DNA double-strand breaks (DSBs) (9, 10). The induction of ICLs by bifunctional alkylating agents therefore disturbs cell cycle progression and triggers cell death. Because the repair of ICLs is a laborious challenge as compared with other DNA damages, the formation of ICLs is the critical step in the cytotoxicity of bifunctional alkylating agents, and is recognized as a critical event in targeting cancer therapies [10,11]. Based on MMC and bis(carbamates)pyrrolizidines, we previously synthesized a series of bifunctional alkylating agents, bis(hydroxymethyl) of 3a-azacyclopenta[a]indene-1-yl, and their bis(methylcarbamate) derivatives (See figure below), and showed potent anticancer activity in a variety of in vitro cell models and in vivo xenograft mouse models [12]. It should be noted that we have filed a disclosure of these bifunctional alkylating agents in a U.S. provisional patent 61/255,620, filed Oct. 28, 2009. Among the series of derivatives of 3a-aza-cyclopenta[a]indenes, BO-1012 and BO-1509 induced a significant level of ICLs and suppressed the growth of human breast carcinoma cells transplanted in nude mice [12].

Among DNA repair inhibitors, arsenic trioxide (ATO) is an antineoplastic chemotherapeutic agent approved for treatment of relapsed or refractory acute promyelocytic leukemia (APL) [13]. ATO has also been reported to reduce cell viability, induce apoptosis, and inhibit tumor growth in myeloma cells at concentrations low enough for safe use in patients [14]. Recent studies have further demonstrated that ATO is highly effective for triggering apoptosis in vitro in a variety of solid tumor cells and for inhibiting tumor growth in xenograft animal models [15]. The promising preclinical activity of ATO against solid tumors supports further investigation of clinical applications for ATO. However, preliminary reports from phase II clinical trials on patients with metastatic renal cell carcinoma [16], and metastatic melanoma [17] suggest that ATO used as a single therapeutic agent may have limited efficacy against solid tumors.
Alternatively, numerous reports have shown that ATO can be used in combination with agents that induce apoptosis [18-20], reduce glutathione [19], inhibit DNA methylation [21], or induce DNA damage [22]. ATO also enhances radiosensitivity to human cervical carcinoma and malignant glioma cells in vitro and in vivo by enhancing autophagic effects and preventing tumor invasion [22-26]. Moreover, a phase II trial of ATO in combination with melphalan and ascorbic acid against myeloma showed that the addition of ATO and ascorbic acid to high-dose melphalan is safe and well tolerated in patients with relapsed or refractory multiple myeloma [24].
Our early studies and others have reported antitumor effects of arsenic compounds on various tumor models [22,25-27]. Numerous studies have shown that arsenic inhibits activity of proteins involved in DNA repair by various mechanisms [28,29], and interferes with both base excision repair and nucleotide excision repair [30]. Qian et al studied arsenic trioxide in the treatment of advanced primary liver and gallbladder cancer [27].
Another DNA repair inhibitor, LY294002 (FIG. 1, a flavonoid derivative) was reported to be able to inhibit DNA repair PI3K or PI3/Akt pathway and possessed antiproliferative and proapoptoic activity in vitro [31]. It was also shown that this agent inhibited tumor growth and induce apoptosis in human tumor cancer xenograft [32,33]. Another AKT inhibitor, triciribine (TCN, nucleoside analogue), was originally found to be a DNA synthesis inhibitor. This nucleoside has been implicated in many human cancers, including prostate carcinomas [34].
Because drug resistance, both inherited and acquired, is a pervasive problem and is a key factor contributing to the failure of clinical chemotherapy, it is of vital importance to develop a regime against cancers that are resistant to DNA damaging agents.